Miniaturized snap acting thermostatic switch

ABSTRACT

A miniature thermostatic switch in which a snap acting thermostatic element having a nondevelopable portion responsible for its snap action is cantilever mounted in a metallic shell. A second mating shell is of electrically insulating material and clamped thereto is an adjustable stationary contact member. In one embodiment the operating temperature of the snap acting thermostatic element is controlled by eliminating creep action prior to snapping of the element by means of a dimple in the metallic shell which applies a bias to the nondevelopable portion of the thermostatic element. In another embodiment the creep action is avoided by forming the entire thermostatic element in the nondevelopable shape.

United States Patent [72] Inventor Antonio Nardulli Marigliano, Naples, Italy [21] Appl. No. 812,699

[22] Filed Apr. 2, 1969 [45] Patented May 4, 1971 [73] Assignee Texas Instruments Incorporated Dallas, Tex.

[32] Priority Apr. 3, 1968 [3 3 Italy [54] MINIATURIZED SNAP ACTING THERMOSTATIC SWITCH 8 Claims, 3 Drawing Figs.

[52] US. Cl 337/89, 337/113, 337/365, 337/372 [51] Int. Cl ..I-I01h37/54 [50] Field ofSearch 337/85, 89,

94, 109 (Cursory), 112, 113, 333, 343, 347, 348, 349,373 (Cursory), 374, 375,377, 378,379 (Curso 'y), 380, 381, 354, 365, 372; 200/166 (ICTS), 67 (D) [56] References Cited UNITED STATES PATENTS 3,430,177 2/1969 Audette 337/365 3,361,883 l/1968 Brassard, Jr. et a1 337/89 Primary Examiner-G. Harris Assistant Examiner-Dewitt M. Morgan Attorneys-Harold Levine, Edward J. Connors, J r., John A.

Haug, James P. McAndrews and Gerald B. Epstein ABSTRACT: A miniature thermostatic switch in which a snap acting thermostatic element having a nondevelopable portion responsible for its snap action is cantilever mounted in a metallic shell. A second mating shell is of electrically insulating material and clamped thereto is an adjustable stationary contact member. In one embodiment the operating temperature of the snap acting thermostatic element is controlled by eliminating creep action prior to snapping of the element by means of a dimple in the metallic shell which applies a bias to the nondevelopable portion of the thermostatic element. In another embodiment the creep action is avoided by forming the entire thermostatic element in the nondevelopable shape.

. v l MINIATURIZED SNAP ACTING THERMOSTATIC I SWITCH BACKGROUND OF THE INVENTION The present invention relates to a miniaturized thermostatic switch device particularly suitable for the protection of the windings of electric motors.

' the power to the motor when the temperature has reached a predetermined maximum limit.

In order to optimize the response time, that is, to minimize the amount of time after the windings reach the predetermined limit and when current to the windings is interrupted, the devices are inserted -directly in contact with the windings of the motor and, consequently, it is important that they be of minimal dimensions and that their sensitivity to overcurrents and overtemperatures be as high aspossible.

In general, because of their particular structure, the prior art devices are of a disproportionate size compared to the motor. As a result, it is necessary to resort to special expedients to mount the devices in the windings of the motor; particularly if it is desired to insert them in small low power appliance motors.

The devices are generally composed of a bimetallic member which deforms itself as a result of the combined joule-radiated temperature effect of the apparatus to be protected causing two contacts to open, interrupting the power supply to the motor.

' The problem of providing a minimum size device is accentua'ted by international electrical standards which specify minimum distances between the contacts and adjacent electrically conductive surfaces. For this reason, devices made out of a metallic housing have inherent limitations in the efficient utilization of space; yet in order to make the device suffrciently sensitive to function as an analog of the windings of the apparatus to be protected, heat from the windings must be transferred to the thermostatic element in the device as effi' ciently as possible. It is therefore very desirable to make at least a portion of the device out of a metallic member and to place the thermostatic element in heat conductive relation therewith.

To make the device more sensitive to ambient temperature, the bimetallic member is generally disposed in the vicinity of the metallic case which also contains all the other parts making up the motor protector, as the snap-action member, contacts, terminals and the insulating body.

SUMMARY OF THE INVENTION It is the object of the present invention to provide a motor protector of very small size, of special sensitivity both to overcurrents and to overtemperatures, wherein the simple arrangement of the individual components brings about, during the opening of the contacts, a suppression of arcs by blasting which insures also under difficult conditions an accurate and correct interruption of the current from the power supply to the apparatus to be protected.

According to the invention, a device is provided which contains in combination a preformed thermostatic element such as a bimetal having a nondevelopable surface, fastened directly on the metallic case of the motor protector to obtain maximum sensitivity to the ambient temperature, and a contact terminal mounted along with a calibrating member on the insulating base, the bimetal and the contact terminal being disposed in parallel relationship to form a small magnetic field to allow the suppression of arcs by blasting which form during the opening of the contacts to extend the life of the contacts.

The device has a cup shaped cover or shell which is provided with dimple extending into the switch cavity. The dimple is arranged to physically contact the central part of the nondevelopable portion of the thermostatic element when the contacts are in engagement. This facilitates the calibration of the switch and improves the accuracy of the operating tem perature at which it snaps as well as avoids creep opening of the contacts prior to snapping of the thermostatic element to. the contacts disengaged position.

BRIEF DESCRIPTION OF THE DRAWINGS or open position, and

Corresponding reference characters indicate corresponding parts throughout the several view of the drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown in the drawings, the thermostatic protection device contains a housing or shell 1 of electrically insulating material which has a closed end portion with side walls depending therefrom. An aperture is provided in the closed end for reception of a first terminal member 2, clasped by the bicornuous portion 3 of member 2 to the closed end of housing I and ending in a stationary contact support arm 4 on which is mounted stationary contact 2a. The position of the fixed contact 2a can be regulated by means of a calibration screw 5 mounted in the closed end of housing I. Arm 4 is cantilever mounted and formed with the distal portion bent out of the general plane of the arm. Calibration screw 5 engages the bent distal portion or arm 4 near the bent line.

It is possible to manufacture the am 4 even completely straight because the'aforementioned bend does not have any specific function.

At the open end of body I a metallic shell 6 is clamped by a flange 7 to an annular flange of housing 1. An extension 12 is provided on shell 6 which forms a second terminal of the device. i

The metallic shell 6 is also provided with a dimple 8 turned inwardly into the switch cavity as shown in FIGS. 1 and 2 for a purpose specified below.

Directly on case 6 a thermostatic element such as bimetallic member 9 is cantilever mounted and carries a movable contact 10 on its distal end. Bimetallic member 9 is formed with a nondevelopable portion 11, making member 9 a snap acting element in a manner conventional in the art.

During initial assembly of the device, movable contact member 2a in the at rest position is moved into physical and electrical contact with stationary contact 10 by calibration screw 5. As screw 5 is moved into the switch cavity, arm 4 is forced toward the open end of housing 1 and force is transmitted through stationary contact 2a to movable contact 10 and in turn, thermostatic element 9 is biased against the dimple 8 to establish a desired prestress to effect calibration of the device. Once calibration has been accomplished, the position of screw 5 can be locked into place by a conventional potting compound.

While in operation, the bimetallic member 9 will execute a small rotation about dimple 8 opening the contacts 2a, 10 with a sudden snap movement and without any prior creep due to the prestress of dimple 8 on portion 11.

Forming the switch cavity with electrically insulating material permits closer spacing of the housing sidewalls while still satisfying the international standards. At the same time, mounting the thermostatic element directly on a metallic cover enhances the heat transfer from the windings of the protected apparatus to the element. This is further enhanced by the physical contact of dimple 8 directly with the nondevelopable portion 11. It will be understood that the device is mounted so that the outer surface of shell 6 is in physical contact with a surface whose temperature is to be sensed or moni- Such a themtostatic element does not tend to creep in the open contacts direction prior to snap action since the entire switch element comprises the nondevelopable portion and therefore dimple 8 in shell 6 can be omitted. The rest of the structure is identical to the FlG. l and 2 embodiment, therefore the detailed description will not be repeated.

in view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

It is to be understoodthat the invention is not limited in its parts illustrated in .the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or ten'ninology employed herein is for the purpose of description and not of limitation.

As'many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense, and it is also-intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

lclaim:

l. A thermostatic switch comprising:

a. a generally cup-shaped housing of electrically insulating material having an open end and a closed end with sidewalls depending therefrom and defining a cavity therein;

b. the end wall of the housing provided with an aperture train;

c. a relatively stiff, generally bicomuous member located in the aperture and having two legs in clamping engagement with the end wall, one leg of the member being elongated and extending substantially across the cavity;

d. a stationary contact mounted on the distal end portion of the member;

e. a second aperture provided in the end wall and receiving therein an adjustable member adapted to engage the elongated leg and bias the leg toward the open end of the housing;

f. a metallic cover enclosing the cavity in the housing;

g. a snap acting thermostatic element having two ends and a nondevelopable portion, the element cantilever mounted by interposing one end between the housing and the cover;

h. a movable contact mounted on the distal end portion of the thermostatic element and adapted to engage and disengage the stationary contact; v

i. an outwardly extending annular flange provided on the distal portion of the housing sidewalls; v

j. the outer peripheral portion of the cover turned radially inwardly about the flange of the housing to clamp the cover to the housing; and

k. a terminal leg extending from the cover.

2. A switch according to claim 1 in which a third leg extends from the bicomuous member outside the housing generally parallel but in an opposite direction to that of the one leg.

3. A switch according to claim 1 in which the one leg of the bicomuous member is formed with a section intermediate the portion in clamping engagement with the housing end wall and the distal end of the one leg, which section is bent out of the general plane of the one leg, the adjustable member aligned to contact the leg section.

4. A switch according to claim 1 in which a dimple is formed in the cover and aligned with the nondevelopable portion of the thermostatic element and in physical contact with the nondevelopable portion only when the contacts are in engagement.

5. A switch according to claim 1 in which the entire area of the thermostatic element extending from the mounting forms the nondevelopable portion.

6. A thennostatic switch comprising:

a. a housing of electrically insulating material and formed with a cavity therein;

b. a metallic cover enclosing the cavity in the housing;

0. a snap acting thermostatic element having a nondevelopable portion responsible for its snap action cantilever mounted in the housing by interposing an end of the element between the housing and the cover with a free end of the element extending into the cavity;

d. a stationary contact mounted in the housing;

e. a movable contact mounted on the thermostatic element so that it is movable into and out of, engagement with the stationary contact; and

. a dimple formed in the cover aligned generally with the center of the nondevelopable portion of the thermostatic element and in physical connection therewith when the contacts are in engagement whereby the thermostatic element pivots about the dimple when the thermostatic element snaps to the open contacts position.

7. A switch according to claim 6 including an adjustable member mounted in the housing and adapted to bias the stationary contact to vary the amount of force exerted on the thermostatic element by the dimple when the thermostatic element is in the contacts closed position.

8. A switch according to claim 6 in which the entire area of the thermostatic element extending from the mounting forms the nondevelopable portion. 

1. A thermostatic switch comprising: a. a generally cup-shaped housing of electrically insulating material having an open end and a closed end with sidewalls depending therefrom and defining a cavity therein; b. the end wall of the housing provided with an aperture train; c. a relatively stiff, generally bicornuous member located in the aperture and having two legs in clamping engagement with the end wall, one leg of the member being elongated and extending substantially across the cavity; d. a stationary contact mounted on the distal end portion of the member; e. a second aperture provided in the end wall and receiving therein an adjustable member adapted to engage the elongated leg and bias the leg toward the open end of the housing; f. a metallic cover enclosing the cavity in the housing; g. a snap acting thermostatic element having two ends and a nondevelopable portion, the element cantilever mounted by interposing one end between the housing and the cover; h. a movable contact mounted on the distal end portion of the thermostatic element and adapted to engage and disengage the stationary contact; i. an outwardly extending annular flange provided on the distal portion of the housing sidewalls; j. the outer peripheral portion of the cover turned radially inwardly about the flange of the housing to clamp the cover to the housing; and k. a terminal leg extending from the cover.
 2. A switch according to claim 1 in which a third leg extends from the bicornuous member outside the housing generally parallel but in an opposite direction to that of the one leg.
 3. A switch according to claim 1 in which the one leg of the bicornuous member is formed with a section intermediate the portion in clamping engagement with the housing end wall and the distal end of the one leg, which section is bent out of the general plane of the one leg, the adjustable member aligned to contact the leg section.
 4. A switch according to claim 1 in which a dimple is formed in the cover and aligned with the nondevelopable portion of the thermostatic element and in physical contact with the nondevelopable portion only when the contacts are in engagement.
 5. A switch according to claim 1 in which the entire area of the thermostatic element extending from the mounting forms the nondevelopable portion.
 6. A thermostatic switch comprising: a. a housing of electrically insulating material and formed with a cavity therein; b. a metallic cover enclosing the cavity in the housing; c. a snap acting thermostatic element having a nondevelopable portion responsible for its snap action cantilever mounted in the housing by interposing an end of the element between the housing and the cover with a free end of the element extending into the cavity; d. a stationary contact mounted in the housing; e. a movable contact mounted on the thermostatic element so that it is movable into and out of engagement with the stationary contact; and f. a dimple formed in the cover aligned generally with the center of the nondevelopable portion of the thermostatic element and in physical connection therewith when the contacts are in engagement whereby the thermostatic element pivots about the dimple when the thermostatic element snaps to the open contacts position.
 7. A switch according to claim 6 including an adjustable member mounted in the housing and adapted to bias the stationary contact to vary the amount of force exerted on the thermostatic element by the dimple when the thermostatic element is in the contacts closed position.
 8. A switch according to claim 6 in which the entire area of the thermostatic element extending from the mounting forms the nondevelopable portion. 